Chopper Transistors

Very Clever. :-)

:>> "John Larkin" wrote in :>> message news: snipped-for-privacy@4ax.com... :>>

:>>>On Thu, 26 Mar 2009 10:52:02 -0000, "Holloway,Graham \\(UK\\)" :>>> wrote: :>>>

:>>>

:>>>>We're paying astronomical prices for 2N2432 and 2N2945's. Does anyone :>>>>happen :>>>>to know of any alternatives worth trying? :>>>>

:>>>>Graham H :>>>>

:>>>

:>>>You mean, short of redesign? There are probably tons of ways to do it :>>>better nowadays... mosfets, jfets, CMOS analog switches, IC chopamps. :>>>

:>>>But Zetex is making some super-low Vce_sat transistors that might work :>>>as choppers. :>>>

:>>>John :>>>

:>>

:>>

:>> Thanks John :>> No option to redesign, customer is happy with everything but the price, :>> design is 35 years old. We have just to get the cost of the parts down. :>> We've got some polycarbonate capacitors costing 160UKP (100+). It goes :>> on. :>>

:>> Graham H :> Perhaps a little talk about reality to the customer is in order. :> Do you want a lower price?...the we can provide a replacement unit that :> is better (give list) at a significantly lower price (and give quote). : :Robert : :This is an ongoing project and time is against us. A new design would cost :big numbers and involve flight qualification. At this time there's not much :money about for new designs. : :Graham H :

The customer has to understand that where an obsolescent design must be kept operative there is no alternative but to pay the going price for the components required to ensure this result.

However, eventually the components required for the old design will become completely unobtainable and the customer (if he wants to support the same functional role) will have no other choice but to re-design using modern techniques and components.

Some people no doubt wanted to retain dinosaurs in the wild too...but, alas, nobody wanted to breed them any more.

It almost sounds to me like a project going into space ("time is against us" and "flight qualification" to name two) as a support component that has been worked out well enough in the past, has experience from past launches, and would need a whole new round of reviews if changed.

Jon

:On Sun, 29 Mar 2009 03:09:50 GMT, Ross Herbert : wrote: : :>On Fri, 27 Mar 2009 09:37:05 -0000, "Holloway,Graham \\(UK\\)" :> wrote: :>

:>:>> "John Larkin" wrote in :>:>> message news: snipped-for-privacy@4ax.com... :>:>>

:>:>>>On Thu, 26 Mar 2009 10:52:02 -0000, "Holloway,Graham \\(UK\\)" :>:>>> wrote: :>:>>>

:>:>>>

:>:>>>>We're paying astronomical prices for 2N2432 and 2N2945's. Does anyone :>:>>>>happen :>:>>>>to know of any alternatives worth trying? :>:>>>>

:>:>>>>Graham H :>:>>>>

:>:>>>

:>:>>>You mean, short of redesign? There are probably tons of ways to do it :>:>>>better nowadays... mosfets, jfets, CMOS analog switches, IC chopamps. :>:>>>

:>:>>>But Zetex is making some super-low Vce_sat transistors that might work :>:>>>as choppers. :>:>>>

:>:>>>John :>:>>>

:>:>>

:>:>>

:>:>> Thanks John :>:>> No option to redesign, customer is happy with everything but the price, :>:>> design is 35 years old. We have just to get the cost of the parts down. :>:>> We've got some polycarbonate capacitors costing 160UKP (100+). It goes :>:>> on. :>:>>

:>:>> Graham H :>:> Perhaps a little talk about reality to the customer is in order. :>:> Do you want a lower price?...the we can provide a replacement unit that :>:> is better (give list) at a significantly lower price (and give quote). :>: :>:Robert :>: :>:This is an ongoing project and time is against us. A new design would cost :>:big numbers and involve flight qualification. At this time there's not much :>:money about for new designs. :>: :>:Graham H :>

:>The customer has to understand that where an obsolescent design must be kept :>operative there is no alternative but to pay the going price for the components :>required to ensure this result. :>

:>However, eventually the components required for the old design will become :>completely unobtainable and the customer (if he wants to support the same :>functional role) will have no other choice but to re-design using modern :>techniques and components. :>

:>Some people no doubt wanted to retain dinosaurs in the wild too...but, alas, :>nobody wanted to breed them any more. : :It almost sounds to me like a project going into space ("time is :against us" and "flight qualification" to name two) as a support :component that has been worked out well enough in the past, has :experience from past launches, and would need a whole new round of :reviews if changed. : :Jon

I have no problem with keeping the old stuff going for as long as it is required. I am simply saying that the customer who wants to go down this path has to pay the going rate for the parts required. Cutting cost is not an option if there isn't anything else which will do the job, so the requirement to "keep costs down" doesn't enter into the argument.

I was making an observation that the "customer" may be a subcontractor looking at the possibility of making a little better profit, without triggering a multi-discipline worthiness review, and asking their minions to scout around for cost cutting possibilities that can be justified by a small amount of paperwork. In other words, it may only be the case that they are investigating what is available in the world... it's possible that although they know _some_ sources, they don't know about _all_ of them. So the question is probably worth a quick ask.

Of course, I'm off on a limb about all this and I otherwise don't think I disagree with you.

Jon

:On Mon, 30 Mar 2009 08:49:37 GMT, Ross Herbert : wrote: : :>On Sun, 29 Mar 2009 09:48:56 GMT, Jon Kirwan wrote: :>

:>:On Sun, 29 Mar 2009 03:09:50 GMT, Ross Herbert :>: wrote: :>: :>:>On Fri, 27 Mar 2009 09:37:05 -0000, "Holloway,Graham \\(UK\\)" :>:> wrote: :>:>

:>:>:>> "John Larkin" wrote in :>:>:>> message news: snipped-for-privacy@4ax.com... :>:>:>>

:>:>:>>>On Thu, 26 Mar 2009 10:52:02 -0000, "Holloway,Graham \\(UK\\)" :>:>:>>> wrote: :>:>:>>>

:>:>:>>>

:>:>:>>>>We're paying astronomical prices for 2N2432 and 2N2945's. Does anyone :>:>:>>>>happen :>:>:>>>>to know of any alternatives worth trying? :>:>:>>>>

:>:>:>>>>Graham H :>:>:>>>>

:>:>:>>>

:>:>:>>>You mean, short of redesign? There are probably tons of ways to do it :>:>:>>>better nowadays... mosfets, jfets, CMOS analog switches, IC chopamps. :>:>:>>>

:>:>:>>>But Zetex is making some super-low Vce_sat transistors that might work :>:>:>>>as choppers. :>:>:>>>

:>:>:>>>John :>:>:>>>

:>:>:>>

:>:>:>>

:>:>:>> Thanks John :>:>:>> No option to redesign, customer is happy with everything but the price, :>:>:>> design is 35 years old. We have just to get the cost of the parts down. :>:>:>> We've got some polycarbonate capacitors costing 160UKP (100+). It goes :>:>:>> on. :>:>:>>

:>:>:>> Graham H :>:>:> Perhaps a little talk about reality to the customer is in order. :>:>:> Do you want a lower price?...the we can provide a replacement unit that :>:>:> is better (give list) at a significantly lower price (and give quote). :>:>: :>:>:Robert :>:>: :>:>:This is an ongoing project and time is against us. A new design would cost :>:>:big numbers and involve flight qualification. At this time there's not much :>:>:money about for new designs. :>:>: :>:>:Graham H :>:>

:>:>The customer has to understand that where an obsolescent design must be kept :>:>operative there is no alternative but to pay the going price for the :>components :>:>required to ensure this result. :>:>

:>:>However, eventually the components required for the old design will become :>:>completely unobtainable and the customer (if he wants to support the same :>:>functional role) will have no other choice but to re-design using modern :>:>techniques and components. :>:>

:>:>Some people no doubt wanted to retain dinosaurs in the wild too...but, alas, :>:>nobody wanted to breed them any more. :>: :>:It almost sounds to me like a project going into space ("time is :>:against us" and "flight qualification" to name two) as a support :>:component that has been worked out well enough in the past, has :>:experience from past launches, and would need a whole new round of :>:reviews if changed. :>: :>:Jon :>

:>I have no problem with keeping the old stuff going for as long as it is :>required. I am simply saying that the customer who wants to go down this path :>has to pay the going rate for the parts required. Cutting cost is not an option :>if there isn't anything else which will do the job, so the requirement to "keep :>costs down" doesn't enter into the argument. : :I was making an observation that the "customer" may be a subcontractor :looking at the possibility of making a little better profit, without :triggering a multi-discipline worthiness review, and asking their :minions to scout around for cost cutting possibilities that can be :justified by a small amount of paperwork. In other words, it may only :be the case that they are investigating what is available in the :world... it's possible that although they know _some_ sources, they :don't know about _all_ of them. So the question is probably worth a :quick ask. : :Of course, I'm off on a limb about all this and I otherwise don't :think I disagree with you. : :Jon

We can glean from the OP's posts that this device is an analogue computer designed 35 years ago and it is used in the aviation industry.

I would imagine that if the function performed by this device is still required in the aviation industry, there must be modern replacements around which can be bought off the shelf and which are currently used by other companies. Surely if there is still a requirement for such devices, their design has been such as to incorporate modern technology and components, including approvals. The UKP3500 for polycarbonate caps alone would go a long way towards a replacement.

I still feel there is a difficulty explaining the time contraints, the prior willingness to pay such prices before, and why it is that they don't see things quite so obviously, regarding the availability of modern replacements with possible approvals already in place. But then all that is only in my imagination.

Jon

Well observed. Although there are no COTS replacements for the function this computer performs. By the way, total component cost is UKP40000.

Graham H

: :Although there are no COTS replacements for the function this :computer performs. By the way, total component cost is UKP40000. : :Graham H :

Seems pretty obvious to me then; there is no COTS replacement for the item, and the total component cost is in the order of UKP40,000. So the device simply has to be kept operational.

This begs the question. "what is the cost of the chopper transistors required?"

I would be surprised if it came to more than 10% of the total cost, even at today's inflated prices for the original type numbers. How important is the cost of the transistors relative to the importance of keeping the thing going? The customer must be made to realise that in a UKP40,000 machine, the "keep the costs down" argument on the transistors can hardly be justified.

cost

..just get transistors that do the same thing correctly and re-brand them... ...then pocket the $ differece.

and

has

required?"

cost

Or implement the whole thing numerically - in a single chip - with e.g. a £5 ADUC7026.

And pocket the £39995 difference :)

and

has

required?"

cost

...and bury the chip inside a nice epoxy-filled can exactly like the original!